Mapping National Parks on the Big Island of Hawai'i

Eric Grossman: surveying the shallow waters of the near-shore by kayak.

Above: Image showing seaward edge of broad pahoehoe platform.

The U.S. Geological Survey (USGS) has recently contracted with the National Park Service to help create an inventory of geologic resources for three parks on the west coast of the Big Island of Hawai'i.

In December 2003, a team of scientists from the USGS' Pacific Science Center in Santa Cruz, CA (Susie Cochran-Marquez, Ann Gibbs, Eric Grossman, and Josh Logan), visited Kaloko-Honokohau National Historical Park, just north of Kona, to collect underwater video footage for use in interpreting existing remotely sensed images.

Building on previously acquired SHOALS (Scanning Hydrographic Operational Airborne Lidar Survey) and aerial photography, the georeferenced data from the camera tows and drops will be incorporated into a Geographic Information System (GIS) layer, with the goal of creating a benthic-habitat map for the offshore areas of the park.

Key areas of the offshore terrain include a broad, shallow platform across most of Honokohau Bay in the southern part of Kaloko-Honokohau National Historical Park. Formed by lava locally referred to as pahoehoe, the platform extends seaward to approximately 3-m water depth. Wave exposure is high in this high-energy zone, and freshwater upwelling is prevalent. Small, hardy corals (for example, Pocillopora meandrina and Porites lobata) are scattered on the pavement throughout the zone.

At the seaward edge of the broad platform is an abrupt drop of approximately 5 m to a mixed zone of boulders and pavement with varying coral cover, pinnacles, and canyons. This mixed zone extends across the deeper mouth of Honokohau Bay and northward throughout the entire region of Kaloko Bay, ranging in water depth from 8 to 15 m.

The steep seaward edge of the mixed zone is densely covered with mostly live and dead finger coral (Porites compressa); it drops off to a gently sloping sandy bottom at 30-m water depth.

In addition to collecting underwater video footage, instruments on the camera-towing package also measured the water's conductivity, temperature, and depth, as well as optical backscatter. These measurements were part of a pilot study to identify and quantify submarine ground-water discharge and the flux of associated nutrients and contaminants to the coastal system.

Future work will include surveys to map the coastal-interface zones of Kaloko-Honokohau National Historical Park, in addition to both coastal and nearshore mapping of the geologic resources of Pu'ukohola Heiau National Historic Site near Kawaihae, and Pu'uhonua O Honaunau (City of Refuge) National Historical Park.

Below left: Three parks on the west coast of the Big Island of Hawai'i being studied by USGS scientists in cooperation with the National Parks Service. NHP, National Historical Park; NHS, National Historic Site.